1. Field of the Invention
The invention relates generally to image display systems, and particularly, to image display systems that reduce the color shift of conventional image display systems.
2. Description of the Related Art
FIG. 1 shows a portion of a conventional display panel. The display panel 100 comprises a red pixel R, a green pixel G, and a blue pixel B. The pixels each comprise a transistor T and a storage capacitor Cst. The gates of the transistors T are coupled to a scan line (Scan). The scan line (Scan) transports a scan signal to control the conductance of the transistors T. The drains of the transistors T of the pixels R, G and B are coupled to data lines Dr, Dg and Db, respectively.
To reduce the total number of pins of a display panel chip, the display panel 100 comprises a demultiplexer 102 and the pixels R, G and B share a single voltage data source (Data). The demultiplexer 102 comprises three switches SWr, SWg, and SWb that are controlled by pulse signals CKHr, CKHg and CKHb, respectively. FIG. 2 shows the driving signals of the display panel 100 (Scan, CKHr, CKHg and CKHb) and the voltage levels of the pixel electrodes of the pixels R, G and B (Vr, Vg and Vb), wherein a row inversion technique is applied to the display panel 100 and for the polarity inversion technique, a common electrode voltage Vcom is provided. When the scan signal transported by the scan line (Scan) is high, the conductance of the transistors T of the pixels R, G and B are high and the voltage data source (Data) sends out voltage data to the pixels R, G and B. Referring to FIG. 2, at time index t1, the pulse signal CKHr turns on the switch SWr and the voltage data sent from Data is transported to the red pixel R (wherein Vr is set to the voltage data), at time index t2, the pulse signal CKHg turns on the switch SWg and the voltage data sent from Data is transported to the green pixel G (wherein Vg is set to the voltage data) and, at time index t3, the pulse signal CKHb turns on the switch SWb and the voltage data sent from Data is transported to the blue pixel B (wherein Vb is set to the voltage data). Because of a voltage coupling effect at the pixel electrodes of the pixels R, G and B, Vr, Vg and Vb mutually affect one another. As shown in FIG. 2, at time index t2, the voltage level of the red pixel electrode (Vr) is shifted by the voltage variation at the green pixel electrode, and symbol 202 marks the shift of Vr. At time index t3, the voltage level of the green pixel electrode (Vg) is shifted by the voltage variation at the blue pixel, and symbol 204 marks the shift of Vg. The variation of Vg (marked by 204) further causes a voltage shift at the red pixel (marked by symbol 206). In this case, the red pixel has the greatest voltage coupling shift because the voltage level of the red pixel electrode (Vr) not only varying with the voltage variation at the green pixel electrode but also varying with the voltage variation at the blue pixel electrode.
As shown in FIG. 2, the voltage data source (Data) provides the same voltage data to the pixels R, G and B. In a case where a normally white technique is adopted such that the liquid crystal material is previous to light when the voltage data applied to it is zero and the luminous intensity of a pixel decreases when the voltage difference between the pixel electrode and the common electrode increases, the red pixel has the lowest luminous intensity and the blue pixel has the greatest luminous intensity. Images displayed by the display panel 100 are biased by a blue color shift. In another case where a normally black technique is adopted such that the liquid crystal material is opaque when the voltage data applied to it is zero and the luminous intensity of a pixel increases with increasing voltage difference between the pixel electrode and the common electrode, the red pixel has the greatest luminous intensity and the blue pixel has the lowest luminance intensity. Images displayed by the display panel 100 are biased by a red color shift.